Image forming apparatus, apparatus for supplying image data to image forming apparatus, and method of interfacing two apparatuses

ABSTRACT

An engine control unit of a printer engine checks the status of each part of the printer, and if there is any change in the status, generates a predetermined representative status of changes and outputs a status change signal to a controller (RIP). The controller is informed of a change in the status by the status change signal, and reads the predetermined representative status to discriminate the changed status from unchanged statuses. In accordance with the discriminated status, the current status can be read. Accordingly, it is not necessary to periodically read the statuses, improving the efficiency of an image forming process. A status change informing control unit in the engine control unit sets a changing status bit of a basic status or status change signal and sends it to the controller, when there occurs a change in any data of a presence/absence and paper size of a paper sheet at a paper feeding port and a loading state of an optional paper feeder. The controller periodically monitors the basic status or status change signal. Only when the changing status bit becomes true, the controller requests the engine control unit to supply the status data representative of a presence/absence, paper size, or loading state of an optional paper feeder.

This application is a division of application Ser. No. 08/603,714 filedFeb. 20, 1996, now pending.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming apparatus, anapparatus for supplying image data to the image forming apparatus, and amethod of interfacing two apparatuses.

2. Related Background Art

FIG. 1 is a schematic diagram showing the structure of anelectrophotographic printer which is one example of conventional imageforming apparatuses. Referring to FIG. 1, reference numeral 100represents a photosensitive drum used as an electrostatic latent imagestoring member. A charger roller 101 is mounted over the photosensitivedrum 100 for uniformly charging the surface of the drum 100 in contacttherewith. A light emission means applies a light beam 104 to thesurface of the photosensitive drum 100 at the charged surfacedownstream, in the rotation direction, of the contact position with thecharger roller 101. The light emission means is constituted by asemiconductor laser 105 for emitting the light beam 104, a scanner 106for scanning the light beam 104 along the surface of the drum 100, andan optical lens 107 for adjusting the light beam to focus it on thesurface of the drum 100 and form a light spot thereon. The light beam104 is modulated with image data to form an electrostatic latent imageon the drum surface. The latent image is developed by a developer 102 toform a toner image, the developer being mounted in contact with thephotosensitive drum 100 further downstream, in the rotation direction,of the position where the light beam 104 is applied.

The toner image is transferred on a sheet of transfer paper P by atransfer roller 103 mounted under the photosensitive drum in contacttherewith. Paper sheets P are stacked in a paper stacker 108 disposed infront (at the right in FIG. 1) of the photosensitive drum 100. A paperfeed roller 109 is disposed at the end portion of the paper stacker 108,facing the left side toward a transport path. Although a single paperstacker is shown in FIG. 1, paper stackers for different paper sizes maybe mounted. Between the paper feed roller 109 and transfer roller 103, aregistration roller 111 is mounted which corrects a slant transport ofthe paper sheet P and synchronizes the image formation on thephotosensitive drum 100 with the paper transport, to thereby transportthe paper sheet P to the transfer position at a predetermined timing. Aregistration sensor 110 is disposed between the registration roller 111and paper feed roller 109 to detect a presence of the paper sheet P.

The paper sheet with the toner image still not developed is furthertransported to a fixing device at the back (at the left in FIG. 1) ofthe photosensitive drum 100. The fixing device is constituted by afixing roller 112 with a fixing device (not shown) being embeddedtherein and a pressure roller 113 for pressing the fixing roller 112.The toner image on the paper sheet still not developed is developed bypressing and heating the paper sheet P transported from the transferarea with the fixing roller 112 and pressure roller 113. An ejectingpaper sensor 114 is mounted at the back of the fixing area, the sensordetecting a paper sheet transported from the fixing area. A paperejecting roller 115 is mounted at the back of the ejecting paper sensor114 to eject the developed paper sheet P.

Next, a control unit of the electrophotographic printer having the abovemechanism will be described with reference to FIG. 2. Referring to FIG.2, reference numeral 200 represents a host computer at the outside ofthe electrophotographic printer. The host computer 200 converts imagecode data entered by a user into parallel or serial data and sends itvia a communication line 201 to a controller 202. The controller 202develops the code data into image data to be transmitted to a printerengine 220, and requests to start printing or paper pre-feeding bysending a command to a printer control unit 203 in the engine 220 or byreading internal data supplied from the printer control unit 203 asstatuses. The controller 202 also controls a sync signal forsynchronizing an image output timing with a paper transport in theprinter. This controller 202 may be installed in the printer or in thehost computer.

The controller 202 is connected to an operation panel 204 from which auser sets various printer modes (e.g., a margin area of an image). Theoperation panel is usually used in an off-line state (disconnected fromthe communication line to the host computer). The controller 202connected to the host computer 200 and operation panel 204 transmitsdata to and from the printer control unit 203 as described above. Inorder to perform a drive/stop timing control of each mechanical partshown in FIG. 1 and read data supplied from each sensor, the printercontrol unit 203 is connected to a transporting system drive unit 205, ahigh voltage drive unit 206, an optical system drive unit 207, a fixingheater control unit 208, and to a sensor input unit 209.

The transporting system drive unit 205 controls a drive/stop of variousmotors 210 and various rollers 211 and the high voltage drive unit 206controls a drive/stop of a charger 212, a fixing device 213, and atransfer unit 214, respectively in response to an instruction from theprinter control unit 204. The optical system drive unit 207 controls adrive/stop of a laser 215 and a scanner 216 and the fixing heatercontrol unit 208 controls a drive/stop of a fixing heater 217,respectively in response to an instruction from the printer control unit204. The sensor input unit 209 reads data from a registration sensor218, an ejecting paper sensor 219, and a paper size sensor 219a, andsupplies the data to the printer control unit 204.

Next, signals transferred between the printer controller 202 and printer(engine) control unit 203 will be described.

Signals to be transferred between the printer controller 202 and enginecontrol unit 203 are as in the following. A signal /CPRDY indicates acommunication ready state between the printer controller 202 and engine220. A signal /PPRDY indicates a communication ready state between theengine control unit 203 and printer controller 202. A signal /RDYindicates a stand-by state allowing the engine control unit 203 to startprinting. A signal /PRNT is a print request signal to be issued from theprinter controller 202 to the engine control unit 203. A signal /VSREQis a request signal for a vertical sync signal to be issued by theengine control unit 203 to the printer controller 202. A signal /HSREQis a request signal for a horizontal sync signal to be issued by theengine control unit 203 to the printer controller 202. A signal /BD is ahorizontal sync signal to be outputted from the engine control unit 203to the printer controller 202. A signal /SCLK is a sync clock signal forserial communication. A signal /CMD is a command signal to be issuedfrom the printer controller 202 to the engine control unit 203. A signal/CBSY is a strobe signal for a command output. A signal /STS indicates astatus on the engine to be issued from the printer controller 202 inresponse to a command. A signal /SBSY is a signal used for outputting astatus. Timings of these signals in serial communications areillustrated in FIG. 3.

When a command /CMD is outputted from the printer controller 202, acorresponding status /STS signal is outputted from the engine controlunit 203. The sync clock /SCLK is outputted from the printer controller101. It is assumed that serial communications are performed in the unitof 8-bit length and LSB is used as the parity bit.

Statuses of the engine control unit 203 in serial communications areillustrated in FIGS. 4A to 4C. STATUS0 is a basic status and indicatesthe fundamental state of the engine 220, STATUS1 and STATUS2 indicatethe details when a "call" bit is "1". STATUS3 indicates the details of amisprint when a "misprint" bit of STATUS0 is "1".

STATUS4 and STATUS5 indicate a paper size of a standard cassette and anoptional cassette (both not shown). STATUS6 indicates a presence orabsence of a paper sheet in each paper feeding unit. STATUS7 indicates apresence or absence of a paper feed function of paper feeding unitsincluding an optional cassette. STATUS8 indicates the contents ofwarning.

In a conventional control using the above statuses, the conditions thatthe signal /RDY becomes "FALSE", i.e., the printer is not in thestand-by state, are satisfied only when one of bits constituting STATUS1and STATUS2 becomes "1" and the "call" bit of STATUS0 becomes "1", orwhen one of bits constituting STATUS3 becomes "1" and the "misprint" bitof STATUS0 becomes "1". Therefore, in order for the printer controller202 to detect a change in STATUS4 to STATUS8 not directly associatedwith the signal /RDY, the printer controller 202 is required to alwaysread STATUS4 to STATUS8.

However, although the printer controller 202 is required to periodicallymonitor these statuses such as paper sizes and a presence or absence ofa paper sheet on a paper feeding port presently not designated, otherthan the data representative of the printer status, particularly theprinter ready status, these statuses are not so often changed under thecircumstances of general users. Therefore, a conventional control isinefficient.

Still further, in the above-described printer system, the printercontroller 202 is required to always read these statuses not directlyassociated with the signal /RDY, so that a process load on the printercontroller 202 increases.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an image formingapparatus which can solve the above problems.

It is another object of the invention to provide an image formingapparatus and an image forming system capable of readily and quicklydetects the contents of any change in statuses in the apparatus.

The image forming apparatus of this invention comprises data processingmeans for processing image data supplied from an external unit, imageforming means for forming an image on a recording medium in accordancewith the image data processed by the data processing means, controlmeans for electrically controlling the image forming means, and meansfor supplying the data processing means with a status change signalgenerated in accordance with at least one change in a plurality ofpredetermined statuses indicating the operation statuses of the imageforming means.

The predetermined status is preferably a status of paper feeding.

The status change signal supplying means preferably generates the statuschange signal in accordance with a change in the plurality ofpredetermined statuses satisfying predetermined conditions.

According to the present invention, since the contents of a change arechecked only after a predetermined status changes. Therefore, other mainprocesses such as image data development can be performed efficiently.

According to the present invention, the statuses in the engine areclassified into a plurality of types (e.g., paper size information,presence/absence information of a paper sheet, option information,etc.), a representative status is provided for respective low levelstatuses, and when there is a change in a low level status, acorresponding bit of the representative status is set to "TRUE".Therefore, even if a status such as a paper size not directly associatedwith a signal /RDY changes, the contents of a change in the status canbe searched with ease.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the structure of a general laserprinter.

FIG. 2 is a block diagram showing the electrical structure of the laserprinter.

FIG. 3 is a timing chart illustrating communications between the printercontroller and the engine control unit.

FIGS. 4A to 4C are diagrams showing examples of statuses to be sent fromthe engine control unit to the printer controller.

FIG. 5 is a schematic diagram showing the structure of a laser printerto which the invention is applied.

FIG. 6 is a block diagram showing a first embodiment of the invention.

FIG. 7 is a flow chart illustrating the operation of the firstembodiment.

FIG. 8 is a block diagram showing a second embodiment of the invention.

FIG. 9 is a flow chart illustrating the operation of a third embodimentof the invention.

FIG. 10 is a schematic diagram showing the structure of a laser printeras one example of the printer of the embodiments.

FIG. 11 is a block diagram showing a print system of a fourth embodimentof the invention.

FIGS. 12A to 12D are diagrams showing examples of statuses to beoutputted from the engine control unit of the fourth embodiment of theinvention.

FIG. 13 is a flow chart illustrating a process to be executed by theprinter controller of the fourth embodiment of the invention uponoccurrence of a status change.

FIG. 14 which comprised of FIGS. 14A and 14B is a flow chartillustrating a process of outputting a status change from the enginecontrol unit of the fourth embodiment of the invention.

FIG. 15 is a timing chart illustrating status transfer of the fourthembodiment of the invention.

FIG. 16 is a timing chart illustrating status transfer of the fourthembodiment of the invention.

FIG. 17 which comprised of FIGS. 17A and 17B is a flow chartillustrating another process of outputting a status change from theengine control unit of the fourth embodiment of the invention.

FIG. 18 is a timing chart illustrating status transfer of a fifthembodiment of the invention.

FIG. 19 is a timing chart illustrating status transfer of the fifthembodiment of the invention.

FIG. 20 is a timing chart illustrating status transfer of the fifthembodiment of the invention.

FIG. 21 is a timing chart illustrating status transfer of the fifthembodiment of the invention.

FIG. 22 is a diagram showing an example of the format of a status changemonitor command of a sixth embodiment of the invention.

FIG. 23 is a diagram showing an example of the format of a status changemonitor command of a seventh embodiment of the invention.

FIG. 24 is a diagram showing an example of the format of a status changemonitor command of an eighth embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the invention will be described with reference to theaccompanying drawings.

(First Embodiment)

The first embodiment will be described with reference to FIGS. 5 to 7.FIG. 5 is a schematic diagram showing the structure of a printer, andlike elements to those shown in FIG. 1 are represented by usingidentical reference numerals.

FIG. 6 is a block diagram showing the structure of the embodiment. Thecharacteristic feature of this embodiment resides in that a statuschange informing control unit is provided in the printer control unit ofthe printer. In FIG. 6, reference numeral 300 represents a hostcomputer, reference numeral 301 represents a communication line,reference numeral 302 represents a controller, reference numeral 303represents a printer control unit, reference numeral 304 represents anoperation panel, reference numeral 305 represents a transporting systemdrive unit, reference numeral 306 represents a high voltage drive unit,reference numeral 307 represents an optical system drive unit, referencenumeral 308 represents a fixing heater control unit, reference numeral309 represents a sensor input unit, reference numeral 310 representsvarious motors, reference numeral 311 represents various rollers,reference numeral 312 represents a charger, reference numeral 313represents a developing unit, reference numeral 314 represents atransfer unit, reference numeral 315 represents a laser, referencenumeral 316 represents a scanner, reference numeral 317 represents afixing heater, reference numeral 318 represents a registration sensor,and reference numeral 319 represents an ejecting paper sensor. Referringto FIGS. 5 and 6, reference numeral 322 represents a paperpresence/absence sensor, and reference numeral 323 represents a papersize sensor. These sensors are provided for each paper stacker anddetects a presence/absence of a paper sheet at a paper feeding port, anda paper size. The detected information is sent to the sensor input unit309. Reference numeral 324 represents an optional feederpresence/absence sensor (not shown in FIG. 5) for detecting apresence/absence of a newly set optional paper feeder and sending thedetected information to the sensor input unit 309.

Referring to FIG. 6, the status change informing control unit 321 checksthe detection results of the sensors 322 and 324, and if there is achange in any one of the data sets representative of a presence/absenceof a paper sheet on each paper feeding port, a paper size, and settinginformation of an optional feeder, then sets a "status change bit" in abasic status, and sends it to the controller 302. The basic status issent, in response to a request from the controller 302, to the printercontrol unit 303 at a constant period. The controller 302 periodicallymonitors the basic status, and when it recognizes the status change bitis TRUE, requests the printer control unit 303 to send the status datarepresentative of a presence/absence of a paper sheet, a paper size, andsetting information of an optional feeder.

The contents of control by the status change informing control unit 321will be described with reference to FIG. 7. The status change informingcontrol unit 321 sequentially monitors (Steps S11, S12, S13) a papersize, a paper presence/absence, at each paper feeding port, and settinginformation of an optional feeder (presence/absence of an optionalfeeder). If there is any change in these data sets from the previousstatus, the unit 321 sets the status change bit in the basic statuswhich is sent to the controller (Steps S21, S22, S23).

(Second Embodiment)

The second embodiment will be described with reference to FIG. 8. Thefundamental structure of the mechanical elements of this embodiment isthe same as that shown in FIG. 5.

FIG. 8 is a block diagram showing the structure of this embodiment.Similar to the first embodiment, the characteristic feature of thisembodiment resides in that a status change informing control unit 421 isprovided in the printer control unit 403 of the printer and that statuschange transmission means 425 is provided. The other structures aregenerally the same as the first embodiment. Reference numerals in the200-order correspond to those in the 300-order of the first embodiment.

The control sequence of the status change informing control unit 421 issimilar to the first embodiment, except Step S22. In the firstembodiment, the status change bit of the basic status is turned ON atStep S22, whereas in the second embodiment, the status changetransmission means 425 is provided which is hardware for informing astatus change from the engine 420 side to the printer controller 402. Inthis manner, a process efficiency of the controller can be furtherimproved, and this embodiment is applicable even if the storage capacityfor statuses is insufficient.

(Third Embodiment)

The third embodiment will be described with reference to FIG. 9. Thefundamental structure of the mechanical elements of this embodiment isthe same as that described with FIG. 5.

A block diagram showing the structure of this embodiment is the same asthe first embodiment (FIG. 6).

The control sequence of the status change informing control unit 421 issimilar to the first embodiment, except Step S22. In the firstembodiment, the status change bit of the basic status is turned ON atStep S22, whereas in this embodiment a status change is informed fromthe engine side to the printer controller side by using a combination ofsignals used for other purposes. In this manner, a process efficiency ofthe printer controller can be improved without raising the cost of thesystem, and the embodiment is applicable even if the number of bits inthe basic status is insufficient.

FIG. 9 is a flow chart illustrating the process of checking the data atthe controller side. A signal /PPRDY is a signal for indicating that theprinter has been initialized after the power-on and serialcommunications with the controller has been enabled. A signal /RDY is asignal for informing the controller of the fact that the conditionsincluding the signal /PPRDY and other print conditions all have beensatisfied. It is obvious that if the signal /PPRDY is FALSE, the signal/RDY necessarily becomes FALSE. In this embodiment, this two signals areused. Specifically, if the signal /RDY becomes TRUE (YES at Step S32)irrespective of whether the signal /PPRDY is FALSE (NO at Step S31),then it is assumed that there is a change in the print conditions. Whenthe controller detects this change, it requests for the statuses of theengine and confirms the contents of the change (Step S33).

(Fourth Embodiment)

A printer connected to, and controlled by, the printer controlleraccording to the fourth embodiment of the invention will be described.

<Structure of Printer>

FIG. 10 shows the mechanism of the printer of the fourth embodiment ofthe invention.

In FIG. 10, reference numeral 1 represents a photosensitive drum forforming an electrostatic latent image, reference numeral 2 represents acharger roller for uniformly charging the photosensitive drum 1,reference numeral 5 represents an optical unit for scanning a laser beamon the photosensitive drum 1, reference numeral 6 represents a laserbeam emitted from the optical unit 5, reference numeral 3 represents adeveloping unit for developing an electrostatic static latent image withtoner, the image being formed on the photosensitive drum 1 by the laserbeam, reference numeral 4 represents a transfer roller charger fortransferring the toner image on the photosensitive drum 1 onto apredetermined paper sheet, reference numeral 7 represents a fixingdevice for fixing the toner image by dissolving the toner on the papersheet, reference numeral 8 represents a standard cassette for stackingprint paper sheets, reference numeral 9 represents a standard cassettepaper feed roller for picking up a paper sheet from the standardcassette, reference numeral 10 represents a manual feed cassette,reference numeral 11 represents a manual feed sheet roller, referencenumeral 12 represents an optional cassette capable of being loaded andunloaded, reference numeral 13 represents an optional cassette sheetroller, reference numeral 14 represents an envelope feeder dedicated toenvelopes, reference numeral 15 represents an envelope feed roller,reference numeral 16 represents an ejecting roller for ejecting a papersheet out of the printer, reference numeral 17 represents a reversingroller for both-side sheet transport, reference numerals 18 and 19represent both-side transport rollers, reference numeral 20 represents asheet re-feed roller for re-feeding the other side of a both-side papersheet, reference numeral 12 represents a registration sensor for theregistration of the start of a transported paper sheet from which aprint starts, reference numeral 22 represents a paper ejection sensorfor detecting whether a paper sheet has been normally ejected out of thefixing device, reference numeral 23 represents a sensor for detecting apresence/absence of a paper sheet on the standard cassette, referencenumeral 24 represents a sensor for detecting a presence/absence of amanually fed paper sheet, reference numeral 25 represents a sensor fordetecting a presence/absence of a paper sheet on the optional cassette,reference numeral 26 represents a presence/absence of an envelope, andreference numeral 27 represents a sensor for detecting apresence/absence of a both-side paper sheet. There are other sensors notshown in FIG. 10 such as a standard cassette size detecting sensor andan optional cassette size detecting sensor.

FIG. 11 is a block diagram showing the printer control unit of thisembodiment.

In FIG. 11, reference numeral 601 represents a printer controller whichcommunicates with the host computer, receives image data, develops thereceived image data into data which the printer can print, performsserial communications with a printer engine control unit to be describedlater, and transfers signals to and from the printer engine controlunit. Reference numeral 602 represents the engine control unit whichtransfers signals to and from the printer controller, and controls eachunit of the printer engine via serial communications. Reference numeral503 represents a paper size detecting unit which detects the size of apaper sheet in a cassette and informs the size data to the enginecontrol unit. Reference numeral 504 represents a paper presence/absencedetecting unit for a paper feeding unit which detects a presence/absenceof a paper sheet at a paper feeding port of a cassette, manual cassette,optional cassette, or envelope feeder, and informs the paperpresence/absence data to the engine control unit. Reference numeral 505represents an option presence/absence detecting unit which detects aconnection state of an optional cassette and envelope feeder. Referencenumeral 506 represents a paper transporting control unit which controlspaper transport. Reference numeral 507 represents an optical systemcontrol unit which controls the optical system including a scanner motorand a laser beam. Reference numeral 508 represents a fixing devicetemperature control unit which controls the temperature, abnormal state,and the like of the fixing device. Reference numeral 509 represents anoption control unit which controls the operation of the optionalcassette and envelope feeder. Reference numeral 510 represents a sensorinput unit which detects registration, ejection, both-sides, reversal,and the like of a paper sheet on the transport path.

A signal /CPRDY 511 indicates a communication ready state between theprinter controller 601 and engine control unit 602. A signal /PPRDY 512indicates a communication ready state between the engine control unit602 and printer controller 601. A signal /RDY 513 indicates a stand-bystate allowing the engine control unit 602 to start printing. A signal/PRNT 514 is a print request signal to be issued from the printercontroller 601 to the engine control unit 602. A signal /VSREQ 515 is arequest signal for a vertical sync signal to be issued by the enginecontrol unit 602 to the printer controller 601. A signal /BD 517 is ahorizontal sync signal to be outputted from the engine control unit 602to the printer controller 601. A signal /SCLK 518 is a sync clock signalfor serial communications. A signal /CMD 519 is a command signal to beissued from the printer controller 601 to the engine control unit 602. Asignal /CBSY 520 is a strobe signal for a command output. A signal /STS521 indicates a status of the engine to be issued from the printercontroller 601 in response to a command. A signal /SBSY 522 is a signalused for outputting a status. A signal /CCRT (Condition Change Report)is a signal which becomes "TRUE" when the contents of statuses of theengine not directly associated with the signal /RDY are changed, tothereby inform the printer controller 602 of the change.

<Statuses of Printer>

FIGS. 12A to 12 D show statuses to be outputted from the engine controlunit of this embodiment.

STATUS0 is a basic status of the engine and contains a "changing status"bit which takes "1" when a status not directly associated with thesignal /RDY representative of a stand-by of the engine control unit ischanged. Such statuses not directly associated with the signal /RDYinclude a cassette size, a presence/absence of a paper sheet in a paperfeeding unit, a presence/absence of a paper feeding function, andwarning. The signal /CCRT becomes "TRUE" when the "changing status" bitbecomes "1".

STATUS1 is a status directly associated with the signal /RDY. STATUS2 isa status constituted by a group of bits representative of a statuschange indicated by the "status changing" bit of /STATUS0. The bitsrepresentative of the status change includes a paper size change, apaper presence/absence change, a function change of paper feeding unit,and a content change of warning. STATUS3 is a status indicating thedetails of a misprint designated by STATUS1. STATUS4 is a statusindicating the details of an operation call designated by STATUS1.STATUS5 is a status indicating the details of a service call designatedby STATUS1.

STATUS6 is a status indicating a standard cassette size. STATUS7 is astatus indicating the optional cassette size. A paper size change bit ofSTATUS2 takes "1" when the contents of STATUS6 or STATUS7 change.

STATUS8 indicates a presence/absence of a paper sheet at each paperfeeding port. The paper presence/absence change bit of STATUS2 takes "1"when the contents of STATUS8 change.

STATUS9 is a status indicating the structure of each paper feeding unitincluding an optional cassette. The paper feeding unit function changebit of STATUS2 takes "1" when the contents of STATUS9 change.

STATUS10 is a status indicating toner absence warning. The warningcontent change bit of STATUS2 takes "1" when the contents of STATUS10change.

When the status not associated with the signal /RDY changes and the"changing status" bit or /CCRT signal becomes "TRUE", the printercontroller 601 checks the contents of STATUS2 to confirm from thechanged bit which part of the status has changed. In this manner, theprinter controller 601 can efficiently search the status changecontents.

FIG. 13 is a flow chart illustrating the process of searching a statuschange to be executed by the printer controller 601.

The controller 601 usually checks the signals /RDY and /CCRT (StepsS301, S302, S312, S313), and when there is a change in these signals, itreads the status information. In this case, if the signal /CCRT is"FALSE" and the signal /RDY is also "FALSE", STATUS1 is first checked(Step S314). In accordance with this check, the lower level statuscorresponding to each bit is referred to and the details are checked(Step S315).

If the signal /CCRT is "TRUE", STATUS2 is first read (Step S302) todiscriminate a changed status or statuses from other unchanged statusesand sequentially read the details of bits of the changed status orstatuses (Steps S304 to S311).

<Reset of Signal /CCRT>

Next, the reset procedure of the signal /CCRT which indicates a statuschange will be described.

FIGS. 14A and 14B are flow charts illustrating the step of generating astatus change status when a change occurs in the status of each engineunit, to be executed by the engine control unit 602.

The engine control unit 602 always checks a change in low levelstatuses, i.e., a change in the paper size, presence/absence of a papersheet, paper feeding unit function, and warning contents. If there is achange, the corresponding bit of the upper level status (STATUS2) is setto "1" And the hardware signal /CCRT is set to "TRUE". Thereafter, thesignal /CCRT is set to "FALSE" after the status change status is read bythe printer controller in response to a status change status requestcommand. The timing when it is assumed that the status change status hasbeen read may be set to either:

(A) when the status change status request command is received; or

(B) when the status change status is transmitted after the status changestatus request command is received.

Each bit of STATUS2 (status change status) is cleared after STATUS2 istransmitted.

FIG. 15 is a timing chart illustrating status transfer at the abovetiming (A), and FIG. 15 is a timing chart illustrating status transferat the above timing (B).

In the case of the timing (A), when a status changes and the signal/CCRT is set to "TRUE" in the process illustrated in FIGS. 14A and 14B,the printer controller 601 detects this signal and issues the statuschange status (STATUS2) request command. Upon reception of the signal/CMD from the printer controller 601, the engine control unit 602 checksif the signal /CMD is the status change status request command. If thestatus change status request command, the signal /CCRT is sent as thesignal /STS. After the status change status (STATUS2) is sent, each bitof STATUS2 and the signal /CCRT are cleared.

In the case of the timing (B), in response to the status change statusrequest command from the printer controller 601, the engine control unit602 sends the status change status (STATUS2). After it is confirmed thatthe status change status has been transmitted to the printer controller601, each bit of STATUS2 and the signal /CCRT are cleared.

As described above, as compared to a conventional periodical statussampling by the printer controller for detecting a status change notassociated with the signal /RDY, this embodiment uses a hardware signal(/CCRT signal) and statuses including the status change status wherein astatus change is first notified by the hardware signal /CCRT andthereafter, one status change status (STATUS2) is read to check aparticular low level status or statuses and read the details thereof.

Therefore, the amount of periodical status check by the printercontroller can be reduced considerably, the image developing process bythe printer controller can be efficiently performed, and the printerperformance can be improved greatly.

(Fifth Embodiment)

The signal /CCRT may be reset by using a reset request signal. FIGS. 17Aand 17B are flow charts illustrating the reset process using the resetrequest signal. In this embodiment, in response to a reset command forresetting status change information sent from the printer controller601, the engine control unit 602 clears the status change status and thesignal /CCRT. The process of checking a status change is similar to theprocess described with FIGS. 14A and 14B. However, resetting the statuschange status (STATUS2) and the signal /CCRT is performed when adedicated status change clear command is received.

FIG. 18 is a timing chart illustrating the reset process using thestatus change clear command. Upon reception of the status change clearcommand from the printer controller 601, the engine control unit 602clears the status change status and sets the signal /CCRT to "FALSE".Thereafter, the basic status STATUS0 is returned back.

With the timing of resetting-the status change status and the signal/CCRT shown in FIG. 18, the printer controller can clear the statuschange information (the signal /CCRT and each bit of the status changestatus) at a desired timing. As shown in FIG. 19, the signal /CCRT maybe reset after the basic status is transmitted.

FIG. 20 is a timing chart illustrating another timing of the embodiment.

In this example, as a method of informing the printer controller 601 ofa status change, the engine control unit 601 sends the /CCRT signalhaving a predetermined pulse width. Therefore, the signal /CCRT iscleared at the timing determined by the engine control unit 602, not bythe status request command or clear command from the printer controller601. Each bit of the status change status may be reset, as shown in FIG.20, after the status is transmitted in response to the status changestatus request command, or may be reset after the status change statusclear command is received as shown in FIG. 21.

As a method of resetting the signal /CCRT, one of the signal /CCRT andthe status change status may be used independently from the statuschange status.

(Sixth Embodiment)

The sixth embodiment is a modification of the fourth and fifthembodiments, only the different points will be described in thefollowing.

In the fourth and fifth embodiments, the signal /CCRT is set to "TRUE"when a status change occurs which makes the "changing status" bit ofSTATUS0 (FIGS. 12A to 12D) turn to "1". In this embodiment, a commandfor designating a status change which makes the signal /CCRT set to"TRUE" is provided.

FIG. 22 shows the format of a status change monitor designating commandto be issued by the printer controller 601. This command is made of twobytes. The first byte is fixed to 7F (HEX). When the first byte isreceived by the engine control unit 601, it recognizes this to be thestatus change monitor designating command, and waits for the secondbyte. The second byte designates the status number by 6 bits binary,excepting a command error bit (MSB) and a parity bit (LSB). For example,0D (HEX) is assigned for designating a lower stage paper size status(status No. 6).

The engine control unit 601 monitors the status number designated by thestatus change monitor designating command, and if the status number ischanged, the signal CCRT is set to "TRUE" (L level), for example, for 10ms. The method of resetting the signal /CCRT may be either that of thefourth embodiment or that of the fifth embodiment. For example, assumingthat the upper stage paper size status (status No. 5) is designated bythe command (7F (HEX)+0B (HEX)), the signal /CCRT is set to L level eachtime the paper size of the upper stage paper cassette is changed.

Next, the monitor control process will be described which is executed bya CPU of the engine control unit 602 when the status change monitordesignating command is received.

It is first checked whether the status change monitor designatingcommand is received from the printer controller 601. If received, thestatus designated by the status change monitor designating command ismonitored. When the contents of the monitored status change, the signal/CCRT is set to L level, for example, for 10 msec.

As described above, the printer controller 601 designates a status ofthe engine control unit 602 whose status change is to be detected,whereas the engine control unit 602 informs the printer controller 601of a change in the contents of the designated status, via the line 523.Therefore, the printer controller 601 is not required to always read thestatus via serial communications using the lines 518 to 521, so that theread communication process can be simplified.

(Seventh Embodiment)

Next, a printer of the seventh embodiment will be described. Thestructure and operation of this printer are similar to the sixthembodiment, and so the description thereof is omitted. FIG. 23 shows theformat of a status monitor mask command used for serial communicationsby the printer of the seventh embodiment.

The status monitor mask command is made of two bytes, and is used withthe status change monitor designating command of the sixth embodiment.The first byte of the status monitor mask command is fixed to 3E (HEX).When the first byte is received by the engine control unit 601, itrecognizes this to be the status monitor mask command, and waits for thesecond byte. The second byte designates the mask positions by 6 bits,excepting a command error bit (MSB) and a parity bit (LSB).

If the mask position bit corresponding to each bit of the statusdesignated by the status change monitor designating command is "1", thenmasking for stopping the status change monitor is performed. If thisvalue is "0", the monitor continues.

For example, assuming that the status change monitor designating commanddesignates the basic status (status No. 0) by the command (7F (HEX)+01(HEX)), the status monitor mask command having the first byte of 3E(HEX) and the second byte of 3E (HEX) is transmitted in order to monitorthe status change of only the print request (second bit). In this case,when the print request bit changes, the signal /CCRT is set to L level,for example, for 10 msec. On the other hand, even if other bits of thebasic status change, the signal /CCRT of H level maintains unchanged.

Next, the monitor control process will be described which is executed bythe CPU of the engine control unit 602 when the status monitor maskcommand is received.

It is first checked whether the status change monitor designatingcommand is received from the printer controller 601. If received, it isfurther checked whether the status monitor mask command is received fromthe printer controller 601. If received, the status monitor mask commandwhose first and eight bits of the second byte (refer to FIG. 23) arechanged to "1" is stored in a RAM as mask data.

If the status monitor mask command is not still received, a logical sumof the status designated by the status change monitor designatingcommand and the mask data is monitored. If the contents of the logicalsum data change, the signal /CCRT is set to L level, for example, for 10msec.

The mask data has a default value of 81 (HEX) which value has no mask ofeach status.

As described above, each bit of the status whose change is to bemonitored can be masked, allowing to monitor each bit of the status.

(Eighth Embodiment)

Next, a printer of the eighth embodiment will be described. Thestructure and operation of this printer are similar to the sixthembodiment, and so the description thereof is omitted. FIG. 24 shows theformat of a status designating command used for serial communications bythe printer of the eighth embodiment.

The status designating command is made of two bytes, and is used withthe status change monitor designating command of the sixth embodiment.The first byte of the status designating command is fixed to 5E (HEX).When the first byte is received by the engine control unit 601, itrecognizes this to be the status designating command, and waits for thesecond byte. The second byte designates status number by 6 bits,excepting a command error bit (MSB) and a parity bit (LSB), so that aparticular number is set to the status designated by the status changemonitor designating command.

For example, assuming that the status change monitor designating commanddesignates the lower stage paper size status (status No. 6) by thecommand (7F (HEX)+0D (HEX)), the status designating command having thefirst byte of 5E (HEX) and the second byte of 1C (HEX) is transmitted inorder to designate a legal paper size. In this case, when legal papersheets are loaded in the lower stage paper cassette, the lower stagepaper size status is set to 1C (HEX) which the engine control unit 602detects, and the signal /CCRT is set to L level, for example, for 10msec.

On the other hand, if paper sheets other than the legal paper sheets areloaded in the lower stage paper cassette, the lower stage paper sizestatus is set to a value other than 1C (HEX) (for example, 01 (HEX) forA4 size), and the signal /CCRT of H level maintains unchanged.

Next, the monitor control process will be described which is executed bythe CPU of the engine control unit 602 when the status designatingcommand is received.

It is first checked whether the status change monitor designatingcommand is received from the printer controller 601. If received, it isfurther checked whether the status designating command is received fromthe printer controller 601. If received, the second byte (refer to FIG.24) of the status designating command is stored in the RAM as designateddata.

It is checked whether the status designated by the status change monitordesignating command coincides with the above designated data. Ifcoincides, the signal /CCRT is set to L level, for example, for 10 msec.

If the status designating command is not still received, the statusdesignated by the status change monitor designating command ismonitored, and when the contents of the status change, the operationsimilar to the sixth embodiment is performed.

As described above, only a change of a desired status to a particularstate is informed to the printer controller 601, further reducing acommunication process load on the printer controller 601.

In the sixth to eighth embodiments described above, the signal /CCRThaving a predetermined pulse width is used. Instead, the signal /CCRTmay be reset by the method described in the fourth or fifth embodiment,or by another method.

In the above embodiments, a printer is used as the image formingapparatus. Instead, a copier may be used as the image forming apparatus.

The invention is applicable not only to a system constituted by aplurality of apparatuses but also to a system having a single apparatus.Obviously, the invention is also applicable to a system or apparatus towhich programs are provided or whose hardware is partially replaced byprograms.

As described so far, the image forming apparatus and system of thisinvention can readily and quickly detect a status change in theapparatus and system. Accordingly, a periodical status check can bereduced considerably and an essential image process of the apparatus andsystem can be efficiently performed. Furthermore, a status change can bechecked only when such a change occurs. Therefore, the controller is notrequired to always monitor all the statuses of the printer while it isperforming the main processes such as image development. Accordingly,the status change can be detected efficiently and the image datadeveloping process or other necessary processes can be executed at highspeed.

In the above embodiments, although an electrophotographic printer isused, the invention is not limited thereto, but other types of printerssuch as ink-jet or thermosensitive printers may also be used.

In the above embodiments, although a vertical sync system by the signals/VSREQ and /VSYNC is used, a system by a signal /TOP (printer engine→controller) may also be used.

The invention is not limited only to the above embodiments, but variousmodifications are possible without departing from the scope of theappended claims. For example, each of the fourth to eighth embodimentsmay be combined with the second and third embodiments. Othercombinations and the like are to be considered as falling within thescope of this invention.

What is claimed is:
 1. A status informing apparatus comprising:interfacemeans for performing interface with an external apparatus, saidinterface means including a plurality of lines connected thereto whichtransmit respective signals that change in signal level in response torespective status changes in said status informing apparatus, firstchanging means for changing the signal level at a first one of theplurality of lines in response to a first type of status change in saidstatus informing apparatus; second changing means for changing thesignal level at a second one of the plurality of lines in response to asecond type of status change in said status informing apparatus; andinforming means for informing the external apparatus of status of saidstatus informing apparatus due to the first and second type of statuschange separately from each other.
 2. An apparatus according to claim 1,wherein the first type of status change is a change from normal statusof said status informing apparatus to abnormal status.
 3. An apparatusaccording to claim 1, further comprising image forming means for formingan image on a recording medium based on image data received from theexternal apparatus.
 4. An apparatus according to claim 3, wherein thesecond type of status change includes a change relating to the recordingmedium set in said apparatus.
 5. An apparatus according to claim 4,wherein the second type of status change includes at least one of achange in size of the recording medium, in presence/absence of therecording medium and in function of a unit for supplying the recordingmedium.
 6. A status monitoring apparatus comprising:interface means forperforming interface with an external apparatus, said interface meansincluding a plurality of lines connected thereto which receiverespective signals that change in signal level in response to respectivestatus changes in the external apparatus, wherein the signals at firstand second ones of the plurality of lines change in signal level inresponse to first and second types of status change in the externalapparatus, respectively; recognition means for recognizing the first andsecond types of status change in the external apparatus based on thesignals at the first and second ones of the plurality of lines; andrequest means for requesting the external apparatus to inform saidstatus monitoring apparatus of status of the external apparatus due tothe first type of status change when said recognition means recognizesthe first type of status change and inform said status monitoringapparatus of status of the external apparatus due to the second type ofstatus change when said recognition means recognizes the second type ofstatus change.
 7. An apparatus according to claim 6, further comprisingmeans for outputting image data to the external apparatus.
 8. Anapparatus according to claim 7, further comprising means for receivinginformation provided in a printer language from a higher level apparatusand means for converting the received information into the image data.9. A system comprising:a status informing apparatus comprising:interfacemeans for performing interface with a status monitoring apparatus, andsaid interface means including a plurality of lines connected theretowhich transmit respective signals that change in signal level inresponse to respective status changes in said status informingapparatus; first changing means for changing the signal level at a firstone of the plurality of lines in response to a first type of statuschange in said status informing apparatus; second changing means forchanging the signal level at a second one of the plurality of lines inresponse to a second type of status change in said status informingapparatus; and informing means for informing the status monitoringapparatus of status of said status informing apparatus due to the firstand second types of status change separately from each other; and saidstatus monitoring apparatus comprising:interface means for performinginterface with said status informing apparatus, through connection tothe plurality of lines of said interface means of said status informingapparatus; recognition means for recognizing the first and second typesof status change in said status informing apparatus based on the signalsat the first and second ones of the plurality of lines; and requestmeans for requesting said status informing apparatus to inform saidstatus monitoring apparatus of status of said status informing apparatusdue to the first type of status change when said recognition meansrecognizes the first type of status change and inform said statusmonitoring apparatus of status of said status informing apparatus due tothe second type of status change when said recognition means recognizesthe second type of status change.
 10. A system according to claim 9,wherein said status informing apparatus further comprises image formingmeans for forming an image on a recording medium, and wherein the firsttype of status change is a change from normal status of said statusinforming apparatus to abnormal status and the second type of statuschange includes a change relating to the recording medium set in saidstatus informing apparatus.
 11. A main apparatus comprising:interfacemeans for performing interface with an external apparatus, saidinterface means including a line connected thereto which transmits asignal that changes in signal level in response to a status change insaid main apparatus, wherein the signal does not change in signal levelin response to a status change from a normal status of said mainapparatus to an abnormal status; detection means for detecting apredetermined status change of said main apparatus different from astatus change from a normal status of said main apparatus to an abnormalstatus; and changing means for changing the signal level at the line inresponse to said detection means detecting the predetermined statuschange.
 12. An apparatus according to claim 11, further comprising meansfor informing the external apparatus of status of said main apparatusdue to the predetermined status change detected by said detection means.13. An apparatus according to claim 11, further comprising image formingmeans for forming an image on a recording medium based on image datareceived from the external apparatus.
 14. An apparatus according toclaim 13, wherein said detection means detects a predetermined statuschange relating to the recording medium set in said main apparatus. 15.An apparatus according to claim 14, wherein said detection means detectsat least one of a change in size of the recording medium, a change inpresence/absence of the recording medium and a change in function of aunit for supplying the recording medium.
 16. An apparatuscomprising:interface means for performing interface with an externalapparatus, said interface means including a line connected thereto whichreceives a signal that changes in signal level in response to apredetermined status change of the external apparatus different from astatus change from normal status of the external apparatus to anabnormal status, wherein the signal does not change in signal level inresponse to the status change from the normal status of the externalapparatus to the abnormal status; recognition means for recognizing thepredetermined status change in the external apparatus based on thesignal at the line; and request means for requesting the externalapparatus to inform said apparatus of status of the external apparatusdue to the predetermined status change when said recognition meansrecognizes the predetermined status change.
 17. An apparatus accordingto claim 16, further comprising means for outputting image data to theexternal apparatus.
 18. An apparatus according to claim 17, furthercomprising means for receiving information provided in a printerlanguage from a higher level apparatus and means for converting thereceived information into the image data.
 19. A system comprising:afirst apparatus comprising:interface means for performing interface witha second apparatus, said interface means including a line connectedthereto which transmits a signal that changes in signal level inresponse to a status change in said first apparatus, wherein the signaldoes not change in signal level in response to the status change fromthe normal status of the external apparatus to the abnormal status;detection means for detecting a predetermined status change of saidfirst apparatus different from the status change from normal status ofsaid first apparatus to abnormal status; and changing means for changingthe signal level at the line in response to said detection meansdetecting the predetermined status change; and a second apparatuscomprising:interface means for performing interface with said firstapparatus, through connection to the line of said interface means ofsaid first apparatus; recognition means for recognizing thepredetermined status change in said first apparatus based on the signalat the line; and request means for requesting said first apparatus toinform said second apparatus of status of said first apparatus due tothe predetermined status change when said recognition means recognizesthe predetermined status change.
 20. A system according to claim 19,wherein said first apparatus further comprises an image forming meansfor forming an image on a recording medium, and wherein said detectionmeans detects a predetermined status change relating to the recordingmedium set in said first apparatus.